It is known in the prior art to upgrade hydrogen deficient petroleum oils to more valuable products by thermal and catalytic cracking operations in admixture with a hydrogen donor diluent material. The hydrogen donor diluent is a material, aromatic-naphthenic in nature that has the ability to take up hydrogen in a hydrogenation zone and to readily release hydrogen to a hydrogen deficient oil in a thermal or catalytic cracking operation.
One advantage of a hydrogen donor diluent operation is that it can be relied upon to convert heavy oils or hydrogen deficient oils at relatively high conversions in the presence of catalytic agents with reduced coke formation. Coke as formed during the cracking operation is usually a hydrocarbonaceous material sometimes referred to as a polymer of highly condensed, hydrogen poor hydrocarbons.
Catalytic cracking systems in use today have taken advantage of new catalyst developments, that is, the use of crystalline zeolite cracking catalysts in preference to the earlier used amorphous silica-alumina cracking catalyst. These new crystalline zeolite cracking catalysts are generally regarded as low coke producing catalysts and have also been found to exercise greater hydrogen transfer activity than the known amorphous silica-alumina cracking catalyst. Thus as the level of coke deposits has been reduced through the use of the crystalline zeolite it has been equally important to concentrate in recovering the maximum amount of heat available through the burning of deposited coke. However, when operating a catalytic cracking process within optimum conditions provided by the crystalline zeolite conversion catalysts, the petroleum refiner is still faced with operating a hydrogen deficient process which does not permit the most optimistic recovery of desired products.
One of the major problems facing refineries in the processing of syncrudes derived from oil shale is the handling of process down-stream of high levels of nitrogen. Nitrogen-containing organic compounds are distributed in various fractions over a broad portion of the shale oil syncrude boiling range. One of their major effects is to poison FCC catalysts, significantly lowering the effective conversion. Similarly, high levels of nitrogen are found in certain petroleum crude stocks, such as the highly naphthenic California coastal crudes. Generally, an appreciable fraction of the nitrogen in such high-nitrogen stocks is contained in the organic structural environment of aromatic-type 5- and 6-membered condensed (polynuclear) heterocyclic rings. Quinoline, indole, carbazol, etc. are some generic representatives of these classes of molecule.